1. Field of the Invention
The present invention relates to a radiation detector, and more particularly to a radiation detector for detecting one or two dimensional intensity distribution of radiation.
2. Discussion of the Background
An X-ray image receptor is used in a facility in which radiation is to be detected, such as a nuclear power plant. The basic structure of the X-ray image receptor and a method of detecting X-rays is described by referring to a perspective view shown in FIG. 1 of a conventional x-ray image receptor. A plate-like scintillator 1 fluoresces in response to received radiation. A plurality of fluorescent fibers 17, such as wavelength-shifting fibers, is arranged in two layers on the rear side of an X-ray reception surface of the scintillator 1. The two layers are arranged so that the fluorescent fibers 17 of one layer are perpendicular to the fluorescent fibers 17 of the other layer. This structure generates and outputs two-dimensional position information of radiation received by the scintillator 1. The fluorescent fibers 17 absorb scintillated light, and irradiate and transmit fluorescent light having a wavelength that is longer than that from the scintillator 1.
If the scintillated light is irradiated from the point of entry of radiation, the fluorescent fibers 17 absorb a part of the scintillated light, thereby fluorescing light. The fluorescent light is transmitted in the fluorescent fibers 17 and is detected by photo detectors (not shown) disposed at the end of the fluorescent fibers 17. The cross point of two fluorescent fibers, in which the fluorescent light is transmitted and detected, is identified as the entry point of radiation.
In the conventional scintillator, the fluorescent fibers 17 are densely arranged in order to achieve high resolution which is approximately equal to the diameter of the fluorescent fibers 17. However, if the number of the fluorescent fibers 17 is reduced and the interval thereof is sparse, the probability of reception of the scintillated light by the fluorescent fibers 17 is thereby reduced. Consequently, the probability of signal detection is lowered.
High resolution is required when detecting X-ray. However, when detecting the distribution of radioactive materials or the distribution of radiation intensity in a conventional nuclear power plant and the like, it is desirable to employ a radiation detector having lower resolution performance and a wider detection range in comparison to that of the X-ray image receptor. That is, although the X-ray image receptor shown in FIG. 1 is used for measuring a range defined by 10-30 millimeter edges, surface contamination inspection in nuclear power plants requires a range defined by 100-300 millimeter edges.
Assume that there exists a basic square having approximately 100 millimeter edges, and that there exists a certain range to be measured containing these basic squares. Here, if the conventional technique as shown in FIG. 1 is employed with sparse arrangement of the fluorescent fibers 17 by reducing the number thereof, practical sensitivity cannot be realized. By contrast, if the number of the fluorescent fibers 17 is increased to a dense arrangement, too many photo detectors and process circuits are required.
The present invention has been made in view of the above-mentioned circumstances and is intended to solve the above-mentioned problems. In particular, an object of the present invention is to provide a radiation detector capable of detecting radiation in a large area.
The present invention provides a radiation detector, including a scintillator that generates a scintillated light in response to received radiation on a first surface of the scintillator. A first light guide is connected to the scintillator, and has a fluorescence characteristic. Each of a plurality of second light guides has a common surface that is arranged at a second surface of the scintillator that is opposite the first surface. The second light guide has a fluorescence characteristic. A plurality of photo detectors is connected to the first light guide and the second light guide for detecting a fluorescent light therein.
The radiation detector may further include a signal processing unit that processes a signal generated by the photo detector in response to the detected fluorescent light.
The first light guide may be connected on the side edge of the scintillator, or may irradiate a fluorescent light which has a different wavelength from that of the scintillated light from the scintillator.
The second light guide may have a surface larger than that of the first light guide, and may be formed of a plate. The second light guide may have a major edge and a minor edge, and the minor edge defines a resolution of detection. The major edge of the second light guide may be approximately the same length as an edge of the scintillator.
The scintillator may have a surface in which the length of the edges thereof is approximately 600 millimeters, and the second light guide may have a surface in which the length of the edges thereof is approximately 100 millimeters and 600 millimeters.
A photo detector may be connected to an end of the first light guide and the second light guide, or may be connected to at least one end of the first light guide.
The radiation detector may further include a reflective material connected to the other end of the first light guide for preventing the leakage of the fluorescent light therefrom.
The first light guide may have a prismatic shape or a circular shape.
The first light guide may include an optical fiber. The scintillator may include a plurality of unit scintillators.
The radiation detector may further include a third light guide for connecting the unit scintillators to each other.
The third light guide may guide each scintillated light from the connected scintillators independently. The third light guide may include a reflective material. A photo detector may be connected to at least one end of the third light guide. The third light guide may be arranged parallel to the first light guide.
The first light guide and the third light guide may be arranged perpendicular to the second light guide. The detector may include a plurality of layers formed of the unit scintillator and the third light guide. The scintillators in the layers may be arranged parallel to each other.
The present invention further provides a radiation detector, including a first detecting layer having a plurality of first scintillators and a light guide. Each first scintillator generates a scintillated light in response to radiation received on a first surface. The light guide has a fluorescence characteristic and is connected to the scintillators. A second detecting layer is arranged on a second surface of the first detecting layer opposite the surface where radiation enters, and has a plurality of second scintillators and a plurality of second light guides. Each second scintillator generates a scintillated light in response to received radiation. The second light guide has a fluorescence characteristic.
The radiation detector may further include a photo detector connected to the light guide and the second light guide for detecting a fluorescent light therein.
The second scintillator may face the opposite side of the surface of the scintillator where radiation is entered, or the second light guide may face the opposite side of the surface of the scintillator where radiation is received.